1. Field of the Invention
This invention relates to a rotary damper for use with a rotating or sliding member such as the lid of an audio or video tape recorder, a computer floppy disk drive, a glove compartment or an ashtray in an automobile or other such device, and which damps rotating or sliding movement of the member.
2. Description of the Prior Art
A typical conventional rotary damper of this type comprises a housing having a chamber filled with a viscous fluid, a cap for covering the housing, a rotor shaft rotatably extending upright from the chamber of the housing and projecting outward from the cap for shearing the viscous fluid by its rotation, and a gear for connecting the rotor shaft and the lid etc. of such a device as mentioned above. In the conventional rotary damper, since the viscous fluid is sheared by the rotation of the rotor shaft, the viscosity of the viscous fluid damps the rotor shaft and consequently the lid etc. of the device via the gear. However, since the conventional rotary damper has a thickness corresponding to the total of the thickness of the housing covered by the cap and the thickness of the gear, it is not suitable for use with such a device as an audio or video tape recorder which is desired to be compact.
As a solution of this problem, Japanese Utility Model Public Disclosure No. 61-136358 proposes a rotary damper of the type wherein a pair of elastic bosses are formed on the body of a device, a gear is inserted under friction on the bosses, and a rack extending from a lid rotatably mounted on the device body is engaged with the gear. This prior art rotary damper, however, can neither maintain a uniform damping force because the damping force relies on the friction resistance between the bosses and the gear nor provide a long service life because the wear at the interface of the bosses and the gear is large.